Portal dosimetry is a technique used in radiation therapy for comparing a planned radiation dose with an actual or delivered radiation dose. Prior to a treatment session (i.e., during a planning phase), a planning image of a treatment area within a patient is generated. The planning image represents a prediction of a portal image that will be obtained during the treatment session. When the actual portal image has been obtained, the planning image and the portal image are compared to identify any differences between the two images. Such differences may be characterized as being either true positive differences or false positive differences. A true positive difference occurs when the radiation dose was not delivered as intended, and adjustments to a treatment plan are likely required. On the other hand, a false positive difference occurs when the radiation dose was delivered as intended, and adjustments to the treatment plan are probably not required.
Unfortunately, due to the large number of variables involved in generating and interpreting the planning images and the portal images, it can be difficult and/or time consuming for a physicist or other user of a portal dosimetry system to distinguish between true positive differences and false positive differences. For example, a gas bubble within the patient may cause a false positive difference, but the physicist may have difficulty recognizing the gas bubble and that the radiation was likely delivered as planned. Likewise, it may be difficult for the physicist to distinguish between a true positive difference caused by displacement of the patient and a false positive difference caused by displacement of an imaging device. Such analyses can take considerable time and incur significant expense.
There is a need for improved systems and methods for interpreting portal dosimetry results. In particular, needs exist for systems and methods that allow physicists to distinguish between true positive differences and false positive differences.